This invention relates generally to battery charger circuits and more particularly to auxiliary alarm circuits for indicating a failure of the battery charger circuit.
Many different types of instrumentalities depend upon a battery to supply power thereto. Accordingly, battery charger circuits are normally included to maintain the battery in a charged state. Many such battery charger circuits obtain charging current from an AC source which is rectified to charge the battery. Occasionally, however, a failure occurs and the battery is not charged properly. Such failures can be attributed to a variety of reasons, such as, for example, the loss of input supply voltage, failure of the voltage rectifier used to rectify AC input voltage in the charger circuit, badly corroded battery terminals or the like.
If the battery from which an instrumentality obtains its power becomes discharged because of any of the aforementioned reasons or others, the loss of power in the battery may not be discovered until too late. Accordingly, failure alarm circuits or circuits to indicate that normal charging is occurring, have been added to the battery charger circuits to warn of any interruption in the normal charging of the battery, hopefully in sufficient time to correct the problem without effecting operation of the instrumentality powered by the battery. Examples of such alarm circuits are shown in British Pat. No. 1,432,567 and U.S. Pat. No. 3,746,961.
In certain, presently available battery charger circuits, a filtering inductor is employed to supply virtually pure DC voltage to the battery being charged by the charger circuit. Accordingly, there is available a continued presence of AC ripple voltage across the inductor so long as there is a proper input supply voltage, an operative rectifier and continuity in the circuit including the battery terminals. If the presence or lack of the AC ripple voltage across the inductor included in the battery charger circuit is utilized correctly, it is possible to determined when the charger circuit ceases to function properly.
The field of a series inductor employed in a battery charger circuit has been used to actuate a magnetic switch for the purpose of completing a circuit to a remote battery being charged and to indicate normal charging of the battery, see U.S. Pat. No. 3,457,491, but no suggestion of the use of the AC ripple voltage across the inductor for any purpose including the operation of a failure alarm circuit, is provided in the patent.